Programmable system on a chip

ABSTRACT

A programmable system-on-a-chip integrated circuit device comprises a programmable logic block, a non-volatile memory block, an analog sub-system, an analog input/output circuit block, and a digital input/output circuit block. A programmable interconnect architecture includes programmable elements and interconnect conductors. Ones of the programmable elements are coupled to the programmable logic block, the non-volatile memory block, the analog sub-system, the analog input/output circuit block, the digital input/output circuit block, and to the interconnect conductors, such that inputs and outputs of the programmable logic block, the non-volatile memory block, the analog sub-system, the analog input/output circuit block, and the digital input/output circuit block can be programmably coupled to one another.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/567,853, filed Dec. 7, 2006, which is a continuation of U.S. patentapplication Ser. No. 10/843,701, filed May 10, 2004, now issued as U.S.Pat. No. 7,170,315, which claims priority from U.S. Provisional PatentApplication Ser. No. 60/491,788, filed Jul. 31, 2003, all of which areincorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to integrated circuits. More particularly,the present invention relates to a system-on-a-chip integrated circuitdevice including a programmable logic block, at least one usernon-volatile memory block, and analog circuits on a single semiconductorintegrated circuit chip, flip chip, face-to-face, or other multiple dieconfiguration.

2. Background

Field-programmable gate array (FPGA) integrated circuits are known inthe art. An FPGA comprises any number of logic modules, aninterconnect-routing architecture and programmable elements that may beprogrammed to selectively interconnect the logic modules to one anotherand to define the functions of the logic modules. To implement aparticular circuit function, the circuit is mapped into the array andthe appropriate programmable elements are programmed to implement thenecessary wiring connections that form the user circuit.

An FPGA includes an array of general-purpose logic circuits, calledcells or logic blocks, whose functions are programmable. Programmablebuses link the cells to one another. The cell types may be smallmultifunction circuits (or configurable functional blocks or groups)capable of realizing Boolean functions of multiple variables. The celltypes are not restricted to gates. For example, configurable functionalgroups typically include memory cells and connection transistors thatmay be used to configure logic functions such as addition, subtraction,etc., inside of the FPGA. A cell may also contain a plurality offlip-flops. Two types of logic cells found in FPGA devices are thosebased on multiplexers and those based on programmable read only memory(PROM) table-lookup memories. Erasable FPGAs can be reprogrammed manytimes. This technology is especially convenient when developing anddebugging a prototype design for a new product and for small-scalemanufacture.

An FPGA circuit can be programmed to implement virtually any set ofdigital functions. Input signals are processed by the programmed circuitto produce the desired set of outputs. Such inputs flow from the user'ssystem, through input buffers and through the circuit, and finally backout the user's system via output buffers referred to as input/outputports (I/Os). Such buffers provide any or all of the followinginput/output (I/O) functions: voltage gain, current gain, leveltranslation, delay, signal isolation or hysteresis. The input/outputports provide the access points for communication between chips. I/Oports vary in complexity depending on the FPGA.

Recent advances in user-programmable interconnect technology haveresulted in the development of FPGAs which may be customized by a userto perform a wide variety of combinatorial and sequential logicfunctions. Numerous architectures for such integrated circuits areknown. Examples of such architectures are found disclosed in U.S. Pat.No. 4,870,302 to Freeman, U.S. Pat. No. 4,758,745 to El Gamal et al.,and U.S. Pat. No. 5,132,571 to McCollum et al. The architecture employedin a particular FPGA integrated circuit will determine the richness anddensity of the possible interconnections that can be made among thevarious circuit elements disposed on the integrated circuit and thusprofoundly affect its usefulness.

Traditionally, FPGAs and other programmable logic devices (PLDs) havebeen limited to providing digital logic functions programmable by auser. Recently, however, FPGA manufacturers have experimented withadding application specific integrated circuit (ASIC) blocks onto theirdevices (See, e.g., U.S. Pat. No. 6,150,837). Such ASIC blocks haveincluded analog circuits (see U.S. Pat. No. 5,821,776). In addition,ASIC manufacturers have embedded programmable logic blocks in theirdevices to add programmable functionality to otherwise hardwired devices(See, e.g., devices offered (or formerly offered) by TriscendCorporation, Adaptive Silicon Inc., and Chameleon Systems.

SUMMARY OF THE INVENTION

A programmable system-on-a-chip integrated circuit device comprises aprogrammable logic block, at least one non-volatile memory block, ananalog sub-system, an analog input/output circuit block, and a digitalinput/output circuit block. A programmable interconnect architectureincludes programmable elements and interconnect conductors. Ones of theprogrammable elements are coupled to the programmable logic block, thenon-volatile memory block, the analog sub-system, the analoginput/output circuit block, the digital input/output circuit block, andto the interconnect conductors, such that inputs and outputs of theprogrammable logic block, the non-volatile memory block, the analogsub-system, the analog input/output circuit block, and the digitalinput/output circuit block can be programmably coupled to one another.

A better understanding of the features and advantages of the presentinvention will be obtained by reference to the following detaileddescription of the invention and accompanying drawings, which set forthan illustrative embodiment in which the principles of the invention areutilized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one illustrative embodiment of asystem-on-a-chip according to one aspect of the present invention.

FIG. 2 is a simplified diagram of a portion of an illustrativeinterconnect architecture that may be used to interconnect the inputsand outputs of the various circuit elements of the system-on-a-chip ofFIG. 1 to form user circuit systems.

FIG. 3 is a block diagram of another illustrative embodiment of asystem-on-a-chip that includes a volatile memory block such as an SRAMblock.

FIG. 4 is a block diagram of another illustrative embodiment of asystem-on-a-chip based on use of a highly successful flash FPGAarchitecture, for the programmable logic block.

FIG. 5 is a block diagram of another illustrative embodiment of asystem-on-a-chip based on use of a flash FPGA architecture for theprogrammable logic block.

FIG. 6 is a schematic diagram of an illustrative glitchless clockmultiplexer that is suitable for use in the SOC of the presentinvention.

FIG. 7 is a block diagram of a portion of the SOC of FIG. 5 showinganalog I/O function circuits grouped into sets according to oneillustrative embodiment of the present invention.

FIG. 8 is a diagram of a pre-scaler circuit that can scale externalvoltages by one of eight factors.

FIG. 9 is a diagram of an illustrative configuration for the amplifierof FIG. 7.

FIG. 10 is a diagram of an illustrative temperature monitor circuit thatmay be usefully employed in the analog I/O function circuit of FIG. 7.

FIG. 11 is a diagram of an illustrative gate drive circuit that may beusefully employed in the analog I/O function circuit of FIG. 7.

FIG. 12 is a diagram of an illustrative embodiment of internal interfacecircuits from FIG. 5 that are particularly useful for the SOC of thepresent invention.

FIG. 13 is a schematic diagram of an illustrative bandgap reference thatmay be used in the SOC of the present invention.

FIG. 14 is a more detailed diagram of the analog-to-digital convertershown in FIG. 5.

FIG. 15A is a power-up sequence state-machine flow chart showing atypical SOC internal power up sequence.

FIG. 15B is a timing diagram showing a typical SOC internal power upsequence.

FIG. 16 is a more detailed block diagram of system supervisor masterblock 140 from FIG. 5.

FIG. 17 is a diagram showing a portion of a power-up control circuitthat may be used in the present invention.

DETAILED DESCRIPTION

Those of ordinary skill in the art will realize that the followingdescription of the present invention is illustrative only and not in anyway limiting. Other embodiments of the invention will readily suggestthemselves to such skilled persons.

The term “system-on-a-chip” or “SOC” generally refers to an integratedcircuit device that includes multiple types of integrated circuits on asingle die, where the circuits are of types that have traditionally beenconstructed on separate silicon wafers.

An SOC 10 according to the present invention design is shown generallyin a block-diagram architectural level drawing in FIG. 1, which showsits main components. As shown in FIG. 1, an illustrative embodiment ofthe present invention is a system-on-a-chip integrated circuit 10 thatincludes a programmable logic block 12, at least one non-volatile memoryblock 14, analog ASIC circuit blocks 16 a through 16 f, digital ASICcircuit blocks 18 a through 18 f, digital input/output (“I/O”) circuitblocks 20 and analog I/O circuit blocks 22. ASIC refers to “applicationspecific integrated circuits” and is used to refer to circuit blocksthat are largely hardwired, in contrast to those that are programmable,writeable, or otherwise able to be modified or configured aftermanufacturing of the device. System-on-a-chip integrated circuit 10 alsoincludes a system controller circuit block 24 and a clock circuit 26.

Programmable logic block 12 may be an FPGA array. FPGA arrays are wellknown in the art, and it is contemplated for purposes of the presentinvention that any type of FPGA circuit block may be employed in thesystem-on-a-chip integrated circuit 10 of the present invention. Thenumber of data inputs and outputs and the number of implementablecombinatorial and sequential logic functions will depend on theparticular design of FPGA circuit used in the FPGA array. Persons ofordinary skill in the art will appreciate that other programmable logicblocks such as complex programmable logic devices (CPLD) and otherprogrammable logic blocks may be used in the present invention.

Non-volatile memory block 14 may be formed from an array of, as anon-limiting example, flash memory cells and a memory controller for thearray. Flash memory cells are well known in the art and the presentinvention is not limited to use of any particular kind of flash memorycells or other non-volatile memory technology, such as nanocrystal,SONOS, solid-electrolyte switching devices, and other types as will beappreciated by persons of ordinary skill in the art. Persons of ordinaryskill in the art will appreciate that, in some embodiments of thepresent invention, non-volatile memory block 14 may be segmented into aplurality of separately addressable arrays, each with its own memorycontroller. The number of data inputs and outputs and address inputswill depend on the size of the array used.

Analog ASIC circuit blocks 16 a through 16 f are illustrated in FIG. 1,although persons of ordinary skill in the art will observe that theprovision of six analog ASIC circuit blocks 16 a through 16 f in FIG. 1is merely illustrative and in no way limiting. Actual embodiments ofsystem-on-a-chip integrated circuits according to the present inventionmay have an arbitrary number of analog ASIC circuit blocks. Analog ASICcircuit blocks 16 a through 16 f may alternatively be described as“hardwired,” “mask programmable,” or “ASIC” circuits or circuit blocks.These analog blocks are also referred to as “analog peripherals,” andmay include, as non-limiting examples, a digital-to-analog converter(DAC), an analog-to-digital converter (ADC), an Analog Pulse WidthModulator (PWM), a MOSFET Controller, a Voltage Reference circuit, aLow-dropout (LDO) regulator, an Analog multiplexer (MUX), or an RFTransceiver. In addition to the more general-purpose types of analogblocks described above, stand alone analog circuit blocks for morespecific functions may be provided, as described above. For example, astand-alone hardwired current monitor, a stand-alone hardwiredtemperature monitor, or a stand-alone hardwired voltage monitor may beprovided. Stand-alone hard analog blocks may include I/O circuits.

Embedded analog peripherals may also be used to enhance genericmicrocontroller (“MCU”) functions with a programmable “soft” processorcore programmed into the programmable logic block. As will beappreciated by persons of ordinary skill in the art, the numbers andkinds of inputs and outputs of the individual analog ASIC circuit blocks16 a through 16 f will depend on the functional nature of the circuitsemployed.

Digital ASIC circuit blocks 18 a through 18 f are illustrated in FIG. 1,although persons of ordinary skill in the art will observe that theprovision of six digital ASIC circuit blocks 18 a through 18 f in FIG. 1is merely illustrative and in no way limiting. Actual embodiments ofsystem-on-a-chip integrated circuits according to the present inventionmay have an arbitrary number of digital ASIC circuit blocks. DigitalASIC circuit blocks 18 a through 18 f may comprise circuit blocks suchas, but not limited to, state machines, analog sequencers,microprocessors, digital signal processors (“DSPs” Hard digital blocksare especially useful to implement interfaces such as the interfacebetween the programmable logic and the memory blocks on a device. TheFPGA/Memory interface is described in more detail in the sectiondescribing the non-volatile memory controller. Hard digital blocks mayalso be used to implement interfaces between the programmable logic orthe memory blocks and hard analog blocks. A hard digital block is usedas a control block for the non-volatile memory block. The non-volatilememory controller is described in more detail herein.

Such digital blocks may be implemented in a similar manner to the way inwhich such digital blocks are implemented in currentapplication-specific integrated circuits (“ASICs”). In addition to beingimplemented as hard digital circuit blocks, all, or a portion of each ofthese types of blocks may be implemented in programmable logic,sometimes referred to as “soft” implementations. As will be appreciatedby persons of ordinary skill in the art, the numbers and kinds of inputsand outputs of the individual digital ASIC circuit blocks 18 a through18 f will depend on the functional nature of the circuits employed.

System-on-a-chip integrated circuit 10 also includes digital I/O circuitblocks 20. Digital I/O circuit blocks 20 may comprise conventionaldigital I/O circuitry, such as that commonly employed in known FPGA andsimilar integrated circuits.

System-on-a-chip integrated circuit 10 also includes analog I/O circuitblocks 22. Analog I/O circuit blocks 22 may comprise any of the manyanalog buffer circuits that are well known in the art.

System-on-a-chip integrated circuit 10 also includes a system controllercircuit block 24. A system controller circuit block 24 provides mastercontrol functionality for the other blocks in the SOC device, includingmanaging power up sequencing and inter-operation of the variouscomponents of the system on a chip. In addition, the system controller24 may control off-chip devices via signals output via the digital oranalog I/Os of the device of the present invention such as reset andenable signals. The system controller 24 includes various circuits formanaging the different functions of the SOC device. In some embodiments,these circuits may all be implemented in hardwired circuit blocks, whilein other embodiments, some of the circuits may be implemented in aportion of the programmable logic of the programmable logic block 12. Anadvantage of implementing control functions in programmable logic isthat the user is able to adapt the control functions to the user'sapplication. This is especially useful if the user wishes to employ theprogrammable system on a chip device to control elements of the user'ssystem that are outside the system on a chip device.

In the embodiment of a system controller shown in FIG. 1, a portion ofthe system controller's circuits are implemented in hardwired blocks,and a portion are implemented in programmable logic. The systemcontroller 24 shown in FIG. 1 includes a power-up control circuit, ananalog power supply circuit, a voltage reference circuit, and a systemsupervisor circuit. The power-up control circuit includes circuitry formanaging the SOC device during power-up, as will be described in moredetail below.

System-on-a-chip integrated circuit 10 also includes a clock circuit 26.Clock circuit 26 may include one or more clock sources andclock-signal-distribution systems. The number of such clocks provided onany system-on-a-chip integrated circuit fabricated according to thepresent invention is a matter of design choice. Such circuits andsystems are well known in the art.

The inputs and outputs of the various circuit elements of theprogrammable logic block 12, a non-volatile memory block 14, analog ASICcircuit blocks 16 a through 16 d, digital ASIC circuit blocks 18 athrough 18 d, digital input/output (“I/O”) circuit blocks 20 and analogI/O circuit blocks 22, system controller circuit block 24 and clockcircuit 26 may be connected together by a user by programmablyconnecting together their various inputs and outputs through a networkof programmable interconnect conductors that is provided on thesystem-on-a-chip integrated circuit.

A simplified diagram of a portion of an illustrative programmableinterconnect architecture that may be employed with the system-on-a-chipintegrated circuit of FIG. 1 is shown in FIG. 2. FIG. 2 illustrates aportion of an illustrative interconnect architecture. Persons ofordinary skill in the art will understand that FIG. 2 is largelyschematic and simplified in nature, and in no way limits the presentinvention to the particular interconnect architecture depicted.

As can be seen from an examination of FIG. 2, an illustrativeinterconnect architecture that can be implemented with the presentinvention may include interconnect conductors that run in horizontal andvertical directions in metal interconnect layers disposed over thesurface of the silicon die comprising the system-on-a-chip integratedcircuit 10. Both the horizontal and vertical interconnect conductors maybe segmented to allow versatility in forming interconnect between inputsand outputs of the various circuit elements disposed in system-on-a-chipintegrated circuit 10 of FIG. 1. As is known in the art, the variousinterconnect conductors may be of varying lengths or may be segmentedinto varying lengths. In addition, either flat or hierarchicalinterconnect systems may be employed.

The segments of the horizontal and vertical interconnect conductors maybe programmably joined together by user-programmable interconnectelements indicated by the circled “X” symbols shown on FIG. 2.Intersections formed by individual ones of the horizontal and verticalinterconnect conductors may also be populated by user-programmableinterconnect elements. The user-programmable interconnect elements maybe in the form of one-time programmable antifuse elements as are knownin the art, or may be in the form of reprogrammable switches as are alsoknown in the art. The latter reprogrammable interconnect switches mayemploy technologies such as flash memory, SRAM, and other knowninterconnect switch technologies.

As shown in FIG. 2, a group 30 of segmented horizontal interconnectconductors is shown crossing a group 32 of segmented verticalinterconnect conductors to form intersections. Persons of ordinary skillin the art will recognize that the horizontal interconnect conductorsand the vertical interconnect conductors are disposed in different metalinterconnect layers of the system-on-a-chip integrated circuit. Anexemplary individual horizontal interconnect conductor is shown to becomprised of segments 34 a, 34 b, 34 c, and 34 d, each adjoining segmentbeing coupled to one another by user-programmable interconnect elements36, 38, and 40, as shown in FIG. 2. Similarly, an exemplary individualvertical interconnect conductor is shown to be comprised of segments 42a, 42 b, 42 c, and 42 d, each adjoining segment being coupled to oneanother by user-programmable interconnect elements 44, 46, and 48, asalso shown in FIG. 2.

Horizontal interconnect conductor segment 34 d is shown intersectingvertical interconnect conductor segment 42 b. The intersection of thesetwo interconnect conductor segments is populated with auser-programmable interconnect element 50.

By programming appropriate ones of the user-programmable interconnectelements, a conductive path may be formed between the output of one ofthe circuit elements on the system-on-a-chip integrated circuit and theinput of another one of the circuit elements on the system-on-a-chipintegrated circuit to form a connection therebetween. Persons ofordinary skill in the art will appreciate that the illustrativeinterconnect architecture depicted in FIG. 2 may appear more or lessregular over areas such as the FPGA array of logic block 12 of FIG. 1and may vary in density, pattern, and/or and direction over other areasand circuit blocks of the system-on-a-chip integrated circuit 10 of FIG.1 as appropriate for the desired connection opportunities.

FIG. 3 is a block diagram of a system-on-a-chip integrated circuit 60similar to the system-on-a-chip integrated circuit 10 shown in FIG. 1,in that it includes a programmable logic block 62, a non-volatile memoryblock 64, analog ASIC circuit blocks 66 a through 66 f, digital ASICcircuit blocks 68 a through 68 f, digital input/output (“I/O”) circuitblocks 70 and analog I/O circuit blocks 72, a system controller circuitblock 74 and a clock circuit 76. System-on-a-chip integrated circuit 60also includes a volatile memory block 78 (e.g., an SRAM block). As inthe embodiment illustrated in FIG. 1, the configuration shown in FIG. 3is simply suggestive of the feature set of a system-on-a-chip integratedcircuit and is not intended to be limiting in terms of the number anddistribution of circuit blocks, layout and other design-choice features.

Another embodiment of an FPGA-based system-on-a-chip 80 is shown in FIG.4. As in the embodiments shown in FIGS. 1 and 3, the FPGA-basedsystem-on-a-chip shown in FIG. 4 includes a programmable logic block 82,a non-volatile memory block 84, analog ASIC circuit blocks 86 a through86 f, digital ASIC circuit blocks 88 a through 88 f, digitalinput/output (“I/O”) circuit blocks 90 and analog I/O circuit blocks 92,system controller circuit block 94 and a clock circuit 96. Thesystem-on-a-chip integrated circuit 80 of FIG. 4 also includes SRAMblock 98. The system-on-a-chip integrated circuit 80 of FIG. 4 alsoincludes a microprocessor 100. In the embodiment of FIG. 4, Flash memoryblock 84 and SRAM block 98 are large enough to allow full use of themicroprocessor. An example of such an embodiment may include amicroprocessor such as an 8051 hardwired core (a popular 1970's 8-bitmicroprocessor with a 16-bit address space) with 64 K-bytes of SRAM and64 K-bytes of flash memory. According to one aspect of the presentinvention, it will be advantageous to configure the SRAM block 98 andflash memory block 84 into separate small blocks (e.g., 1K, 2 k, or 4K)and allow them to be programmed into the address space of themicroprocessor 100 as desired. In such an embodiment, memory blocks thatare not used by the processor could be allocated for use by the FPGAblock 82 of the circuit.

According to another aspect of the present invention, a moresophisticated microprocessor or microcontroller, a system bus and otherfeatures like timers, UARTs, SRAM or DRAM ports, etc., may be provided.The SRAM may operate under DMA mode for the microprocessor. An FPGA orother programmable logic device, including a microprocessor (soft orhard) requires memory for program store. Because program-store memorynever changes, an on-board PROM program-store block is useful for thistask. PROM memory has an advantage as it is much denser than SRAM anddoes not need to be loaded from some external source. The PROM howevermay be quite slow, so a SRAM cache may be provided for the fastprocessor into which the PROM program-store is loaded (perhaps inparallel or in the background) such that the entire PROM would not needto be duplicated in SRAM. There are well known methods for a processorto download blocks of memory to the cache as they are needed.

SRAM-based FPGA is typically configured by a bit-stream that is storedin non-volatile memory, by integrating a microcontroller and flash FPGAin one chip. The microcontroller can take the control of FPGAre-configuration for certain applications during boot-up or on-the-flysystem operation. On the other hand, the configuration procedure can bereversed to let the FPGA set up the microcontroller, for example, if thesystem times out or hangs during operation, the FPGA can send a softreset to the microcontroller instead of requiring a hard reset. Both themicrocontroller and FPGA blocks share on-chip SRAM, which can bedesigned as dual-port SRAM to be accessed synchronously. In order toreduce data latency, on-chip SRAM can work under DMA mode for themicrocontroller. Customized instructions can be implemented in flashmemory, or FPGA blocks can be reconfigured as a co-processor eitherthrough the on-chip microcontroller or external host to build a powerfulflash-based FPGA on-chip processor platform.

One particular embodiment of the invention may be configured using ahighly successful flash FPGA architecture as the programmable logicblock 12 of FIG. 1. An example of such an architecture may be found inthe ProASIC line of FPGA integrated circuits available from ActelCorporation of Mountain View, Calif. By combining an advanced flash FPGAcore with embedded flash memory blocks or analog peripherals,system-on-a-chip devices according to the present invention dramaticallysimplify system design, and as a result, save both board space andoverall system cost. The state-of-the-art flash memory technology offersvery high-density integrated flash arrays and therefore a substantialcost saving over use of external flash chips to configure SRAM-basedFPGAs, the traditional alternative. The multiple analog circuit blocksextend the traditional FPGA application from the purely digital domainto mixed-signal applications. The embedded flash memory and integratedanalog circuit blocks can be used with an integrated soft (i.e.,configured from programmable logic) processor to implement a fullfunctional flash microcontroller unit (MCU), or the advanced analogcircuit blocks can be used with high speed FPGA logic to offer systemand power supervisory abilities.

Such an embodiment of the present invention is illustrated in the blockdiagram of FIG. 5. SOC 110 includes a field-programmable gate array(FPGA) that includes an FPGA core 112 comprising logic tiles, routing,and flash-cell switches and programming structures and techniques as isknown in the art. General-purpose input/output (GPIO) circuits 116 maybe coupled to the FPGA core 112 through I/O tiles 114 as is known in theart.

A clock generator circuits block 118 and distribution system is includedto provide an on-chip source for clock signals. The clock generatorcircuits block 118 may include RC oscillators. One or more of thesemoderate precision (1-2%) clock sources may be completely containedwithin the SOC 110 and may be used for internal charge pumps and NVMerase/program timing. They can also be the source of clocks for the FPGAand/or the external system where precise frequency control is notneeded. The clock generator circuits block 118 in SOC 110 of the presentinvention may also include a crystal oscillator circuit. This relativelyhigh-precision clock source (˜100 PPM) requires an inexpensive externalcrystal that may be connected to the SOC 110 through a pair of I/O pinsas shown in FIG. 5. The clock-generator circuits block 118 can be usedfor all FPGA and system clock requirements. The SOC may further includeone or more phase locked loops (PLLs) 120.

In addition, clock generator 118 of the SOC 110 of FIG. 5 may alsoinclude a glitchless clock multiplexer to allow clean switching betweenmultiple internal or external clock sources. The glitchless clockmultiplexer may be used to provide a selectable low power (lowfrequency) mode to on-chip clocked systems, or to switch between clocksfor any other application reason. This can save board space in a systemin which the SOC is used and provides a reliable clock source forcritical system management functions. An illustrative clock multiplexerwill be described with reference to FIG. 6.

A flash programming circuit 122 for programming the FPGA, is coupled toa JTAG TAP controller 124, designed in accordance with the JTAGstandard, for entering the programming data through a JTAG port 126 todefine the configuration of the FPGA circuits as is known in the art. Asecurity circuit implementing an encryption/decryption algorithm may beprovided. For example, decryption circuit 128 may be a circuit designedto implement the AES encryption/decryption standard. The AdvancedEncryption Standard (“AES”) (FIPS PUB 197) National Institute ofStandards and Technology (NIST), Gaithersburg, Md., is available fromNational Technical Information Service (NTIS), 5285 Port Royal Road,Springfield, Va. 22161. The Advanced Encryption Standard (AES) specifiesa cryptographic algorithm that can be used to protect electronic data.The AES algorithm is a symmetric block cipher that can encrypt(encipher) and decrypt (decipher) information. The AES algorithm iscapable of using cryptographic keys of 128, 192, and 256 bits to encryptand decrypt data in blocks of 128 bits. The algorithm specified in thisstandard may be implemented in software, firmware, hardware, or anycombination thereof. The specific implementation may depend on severalfactors such as the application, the environment, the technology used,etc. Encryption can be used to protect the FPGA configurationinformation, the contents of the non-volatile memory, etc.

GPIO circuits that would normally be disposed along the lower edge ofthe FPGA core are shown replaced in FIG. 1 by internal interfacecircuits 130 for making connections between the FPGA core 112 and theother SOC circuit blocks. According to one aspect of the presentinvention these GPIO circuits and interface blocks may be in the form of“tiles” having identical footprints.

SOC 110 also includes at least one non-volatile memory (NVM) block. Inthe illustrative embodiment of the present invention shown in FIG. 5there are two NVM blocks 132 and 134 that are stand-alone flash memoryarrays. According to another aspect of the present invention, the flashmemory arrays are preferably sized between about 64 kBytes to about 512kBytes. Each of flash memory arrays 132 and 134 has built-in knowncharge pumps and programming circuits to allow each to operateindependently from the other and from the FPGA core. The provision ofmore than one flash memory block permits the SOC 110 of FIG. 5 tosimultaneously perform two separate system functions using non-volatilememory. In the illustrative embodiment of the invention shown in FIG. 5,timing input is provided to the flash memory blocks from the on-chipclock generator circuits 118 for accurate/reliable programming and eraseof each flash memory array 132 and 134.

According to another aspect of the present invention, provision is madefor several possible NVM programming paths for NVM blocks 132 and 134,including through the FPGA from data sources in the FPGA core 112,through the FPGA core from data sources outside the FPGA core 112through the GPIO 116, directly from the JTAG port 124 from external JTAGmasters (such as an FPGA programmer), and data streams decrypted by theAES block 126 from JTAG data sources. The FPGA to NVM module interfaceprovides JTAG full capture and control boundary scan registerfunctionality. A boundary scan register can directly control and captureall core to NVM inputs and can capture all NVM outputs in a manner knownin the boundary-scan art.

According to another aspect of the present invention, the NVM blocks 132and 134 can be used to store data appropriate to provide power-upinitialization of FPGA memories, analog-to-digital converter (ADC)functions, system-wide power up functions, program storage formicrocontrollers or microprocessors, and general data storage as isknown in the art.

The SOC 110 of FIG. 5 also includes an ADC 136. According to oneillustrative embodiment of the invention, the ADC may select from one ofa plurality of multiplexed analog inputs and converts the appliedvoltage to an equivalent digital value. The ADC may also includeselectable conversion resolution (e.g., 8, 10, or 12 bit conversion).According to one illustrative embodiment of the invention, a voltagereference input at the input of ADC 136 corresponds to full-scaleoutput. As will be further disclosed herein, ADC 136 may include amultiplexer coupled to its input to allow multiple analog voltagesources to be used. The ADC 136 is coupled to analog I/O 138. Analog I/O138 is also coupled to interface tiles 130 as will be more fullydisclosed herein.

The SOC 110 of FIG. 5 also includes a system supervisor master block140. System supervisor master block 140 includes an on-chip power upblock 142, analog voltage supply charge pumps 144, an on-chip voltagereference 146 and a system supervisor block 148.

Referring now to FIG. 6, an illustrative glitchless clock multiplexer150 that is suitable for use in the SOC of the present invention isshown. Glitchless clock multiplexer 150 may be used to select between a“Clock A” input at line 152 and a “Clock B” input at line 154 by use ofa select line 156. The clock A input 152 drives the clock inputs of datalatches 158 and 160 and one input of AND gate 162. Select line 156 iscoupled to one input of an AND gate 164 whose output drives the datainput of data latch 158.

Similarly, the clock B input 154 drives the clock inputs of data latches166 and 168 and one input of AND gate 170. The data output of data latch168 drives the other input of AND gate 170. Select line 156 is coupledto one (inverted) input of an AND gate 172 whose output drives the datainput of data latch 166. The output of AND gate 170 drives the other(inverted) input of AND gate 164 and the output of AND gate 162 drivesthe other (inverted) input of AND gate 172. The outputs of AND gates 162and 170 drive inputs of OR gate 174. Persons of ordinary skill in theart will observe that the circuit of FIG. 6 allows selecting between theclock inputs A and B without producing any glitches at the output of ORgate 174.

As previously mentioned, analog I/O circuits 138 in FIG. 5 are used toprovide inputs and outputs to ADC 136. According to one illustrativeembodiment of the present invention, shown in FIG. 7, analog I/Ofunctions may be grouped into sets. Analog I/O circuits 138 may containa number of these sets.

The set of analog I/O circuits shown in FIG. 7 has four members. Personsof ordinary skill in the art will realize that FIG. 7 is illustrativeonly, and a set of analog I/O circuits in an actual SOC may have feweror more members. In the embodiment illustrated in FIG. 7, a first member180 of the set may be a voltage input block coupled to I/O pad 182. I/Opad 182 that may either have a direct connection to the input of ADC 136(or one input of its input multiplexer), or may be connected to itthrough a buffered prescaler circuit 184. Prescaler circuit 184 may havea programmable gain set to 1 of n selectable values as will be disclosedfurther herein. Multiplexer 186 is employed to select between the directinput or the prescaled input. The select inputs of multiplexer 186 maybe controlled from the FPGA. According to another aspect of the SOC ofthe present invention, I/O pad 182 can be configured through digitalinput circuit 188 as a low-performance digital input to the FPGA core.

A second member 190 of the set may be a current-monitor input blockcoupled to I/O pad 192. Like I/O pad 182, I/O pad 192 may either have adirect connection to the input of ADC 136 (or one input of its inputmultiplexer), or may be connected to it through a buffered prescaler194. Like prescaler 184, prescaler 194 may have a programmable gain setto 1 of n selectable values as will be disclosed further herein.Multiplexer 196 is employed to select between the direct input from I/Opad 192 or the prescaled input. The select inputs of multiplexer 196 maybe controlled from the FPGA. Like I/O pad 182, I/O pad 192 can beconfigured through digital input circuit 198 as a low-performancedigital input to the FPGA core.

In addition to the functions that are identical to that for I/O pad 182,set member 190 may be used to measure the difference between I/O pad 182and 192. This may be used to measure a voltage drop across a smallresistor in series with an external power supply. I/O pad 192 isconnected to one input of an amplifier 160. The other input of amplifier198 is coupled to I/O pad 182. The output of amplifier 160 is presentedto a third input of multiplexer 194. If a low value (e.g., 0.1 ohms)resistor (not shown in FIG. 7) is coupled between I/O pads 182 and 192,and a voltage supply potential is coupled to I/O pad 182 and a load iscoupled to I/O pad 192, the voltage drop across that resistor can besensed and amplified by amplifier 200. That voltage drop is directlyproportional to the current flowing through the resistor. Anillustrative configuration for amplifier 160 is shown and described withreference to FIG. 9.

A third member 210 of the set may be a temperature-monitor input blockcoupled to I/O pad 212. Like I/O pad 182, I/O pad 212 may either have adirect connection to the input of ADC 136 (or one input of its inputmultiplexer), or may be connected to it through a buffered prescaler214. Like prescaler 184, prescaler 214 may have a programmable gain setto 1 of n selectable values as will be disclosed further herein.Multiplexer 216 is employed to select between the direct input from I/Opad 210 or the prescaled input. The select inputs of multiplexer 216 maybe controlled from the FPGA. Like I/O pad 182, I/O pad 212 can beconfigured through digital input circuit 218 as a low-performancedigital input to the FPGA core.

In addition to the functions that are identical to that for I/O pad 182,set member 210 may be used as a temperature monitor for a signal on I/Opad 212. This set member 210 may be configured to measure temperature ofan external diode by taking advantage of the temperature behavior of theI-V characteristics of a diode. A temperature monitor circuit 220 mayalso be coupled to an input of multiplexer 216. The SOC of the presentinvention may be supplied with a plurality of temperature monitorcircuits. According to one embodiment of the invention, a number oftemperature sensors are for measuring external temperature (e.g., thejunction temperatures of other ICs or air temperature) and one formeasuring its own junction temperature. Temperature monitor circuit 220is explained in more detail with reference to FIG. 10.

A fourth member 230 of the set may be a gate-driver output block coupledto I/O pad 232. Power MOSFET gate driver circuit 234 drives I/O pad 232from the FPGA. I/O pad 232 may be coupled to I/O pad 232 and/or I/O pad212 through either of pullup resistors 236 and 238, respectively.Persons of ordinary skill ion the art will realize that resistors 236and 238 are optional. An optional ramp resistor 200 may be coupled toI/O pad 232 or I/O pad 212. Gate driver circuit 234 is explained in moredetail with reference to FIG. 11.

According to one embodiment of the present invention, the pre-scalercircuits 184, 194, and 214 are provided to scale external voltages up ordown. Referring now to FIG. 8, a pre-scaler circuit is shown that canscale external voltages by one of eight factors. The pre-scaler circuitcan be used in voltage monitor functions or in any analog inputfunctions. The pre-scaler circuit may be based upon a current mirrorcircuit. A first side of the current mirror circuit including a resistor250 coupled between I/O pad 192 and diode-connected n-channel MOStransistor 252. The gate and drain of diode-connected n-channel MOStransistor 252 are connected to the gates of n-channel MOS transistors254, 256, 258, and 260. The ratios of the width of diode-connectedn-channel MOS transistor 252 to the widths of n-channel MOS transistors254, 256, 258, and 260 are selected to produce the desired scalingfactors.

The sources of n-channel MOS transistors 254, 256, 258, and 260 arecoupled to a fixed potential, such as ground, through enable n-channeltransistors 262, 264, 266, and 268, respectively. The gates of enablen-channel transistors 262, 264, 266, and 268 are driven from a decodercircuit 310. The control lines of decoder circuit 310 are driven fromthe FPGA array. The drains of n-channel MOS transistors 254, 256, 258,and 260 are coupled together to the non-inverting input of operationalamplifier 312. Resistor 314 sets the gain of operational amplifier 312.

According to one aspect of the invention, the following voltage-scalingfactors: 0.20161, 0.40322, 0.80645, 1.6129, 3.2258, 6.45161, 12.90322,and 25.80645 have been found to be particularly useful. This isparticularly useful where the full-scale voltage of ADC 136 of FIG. 5 is3.3V. The choice of these eight scaling factors is controlled by threebinary control signals coming from the FPGA. Using these factors 16V canbe scaled down to 3.3V using the factor 0.20161 (16*0.20161=3.3) and 125mv can be scaled up to 3.3V using the factor 25.80645(0.125*25.80645=3.3). Also the pre-scaler can scale negative voltages topositive voltages (i.e. −16V can be converted to 3.3V). Hence thefunction of the pre-scaler is to convert input voltages into ranges thatare acceptable by the ADC. The reason for employing the exemplaryscaling factors recited herein is for user convenience to achievecorrespondence between the digital output of the ADC and one-millivoltsteps. From an examination of this disclosure, persons of ordinary skillin the art will appreciate that any number of different scaling factorsmay be selected.

An illustrative configuration for amplifier 200 of FIG. 7 is shown anddescribed with reference to FIG. 8. External resistor 280 is showncoupled between I/O pads 142 and 192. By the initial positions ofswitches 282, 284, 286, and 288 (shown in FIG. 8), the offset value ofthe operational amplifier 290 is stored in capacitor 292 so that theoutput of the operational amplifier 250 is approximately at ground. Alsothe capacitors 294 and 296 are charged to the voltage level which is atthe right side of the external resistor 280 and the non-inverting inputof the operational amplifier 290 is at ground. The inverting input ofoperational amplifier 290 is at virtual ground. Switches 282, 284, 286,and 288 are then switched in order (first switch 282, then switch 284,then switch 286, then switch 288). After all the switches 282, 284, 286,and 288 are at their new positions, the voltage drop across the externalresistor 280 is amplified by the operational amplifier 290 with a gaindefined by (C₂₅₆+C₂₅₈)/C₂₅₈. The output voltage of the operationalamplifier 290 is applied to the input of the ADC. Since the value of theexternal resistor value is known, the current through the externalresistor is known. The configuration of the circuit of FIG. 9 has theadvantage of avoiding amplifying the voltage offset of operationalamplifier 290.

Referring now to FIG. 10, temperature monitor circuit 220 is explainedin more detail. This circuit forces two different currents through adiode and measures the voltage drop difference across the diode. It thenamplifies this voltage by a factor of five and sends it to the ADC. Thisamplified voltage difference directly corresponds to temperature (in °K.).

For example, as shown in FIG. 10, a voltage difference of 59.6 mV(corresponding to diode temperature of 25° C.) is measured bysequentially forcing 10 uA and 100 uA across diode 300. This isamplified 5X—which gives 298 mV—which corresponds to 298K (25C). Diodeis coupled to I/O pad 212. Two current-generating circuits are shown,allowing the diode 300 to be oriented in either direction. The firstcurrent-generating circuit which sources current includes a first legincluding p-channel MOS transistors 302, 304, and 306 coupled in seriesbetween a supply potential of +3.3 VDC and the I/O pad 212. The gate oftransistor 302 is coupled to a positive bias potential. The gate oftransistor 304 is coupled to ground and the gate of transistor 306 iscoupled to a Source/Sink control signal. The sizes of transistors 302,304, and 306 and the value of the positive bias potential are chosen tocause 10 μA to flow (source) through diode 300.

The second leg in the first current-generating circuit includesp-channel MOS transistors 308, 310, and 312 coupled in series betweenthe supply potential of +3.3 VDC and the I/O pad 212. The gate oftransistor 308 is coupled to the positive bias potential. The gate oftransistor 310 is coupled to a control signal “S” and the gate oftransistor 312 is coupled to the Source/Sink control signal. The sizesof transistors 308, 310, and 312 and the value of the positive biaspotential are chosen to cause an additional 90 μA to flow (source)through diode 300.

Similarly, The second current-generating circuit which sinks currentincludes a first leg including n-channel MOS transistors 314, 316, and318 coupled in series between a supply potential of −3.3 VDC and the I/Opad 212. The gate of transistor 314 is coupled to a negative biaspotential. The gate of transistor 316 is coupled to a positive voltageand the gate of transistor 318 is coupled to the Source/Sink controlsignal. The sizes of transistors 314, 316, and 318 and the value of thenegative bias potential are chosen to cause 10 μA to flow (sink) throughdiode 300.

The second leg in the first current-generating circuit includesn-channel MOS transistors 280, 282, and 284 coupled in series betweenthe supply potential of −3.3 VDC and the I/O pad 212. The gate oftransistor 280 is coupled to the negative bias potential. The gate oftransistor 282 is coupled to the control signal “S” and the gate oftransistor 284 is coupled to the Source/Sink control signal. The sizesof transistors 280, 282, and 284 and the value of the negative biaspotential are chosen to cause 90 μA to flow (sink) through diode 300.

If the Source/Sink control signal is low, the current sourcingtransistors operate. If the Source/Sink control signal is high, thecurrent sinking transistors operate. In either case, the first leg ofthe circuit (either transistors 302, 304, and 306 or transistors 314,316, and 318) are turned on, sourcing or sinking 10 μA through diode300. When the “S” (or “S!”) signal is asserted, the second leg of thecircuit (either transistors 308, 310, and 312 or transistors 320, 322,and 324) is also turned on, sourcing or sinking a total of 100 μAthrough diode 300.

The remaining components of the circuit include operational amplifier326 having its non-inverting input grounded, capacitor 328 coupledbetween I/O pad 212 and the inverting input of operational amplifier326, and capacitor 330, coupled between the inverting input ofoperational amplifier 326 and its output through n-channel MOStransistor 332. In the example of FIG. 10, capacitor 328 has five timesthe capacitance of capacitor 330, which determines the gain of thecircuit. Capacitor 330 stores and thus cancels the offset of operationalamplifier 326.

The common connection of capacitor 330 and transistor 332 is coupled toground through n-channel MOS transistor 334. The gate of transistor 332is coupled to a control signal Y! and the gate of transistor 334 isconnected to a control signal Y. An n-channel MOS transistor 336 iscoupled between the inverting input sand the output of operationalamplifier 326 and has its gate coupled to a control signal X. Ann-channel MOS transistor 338 is coupled to the inverting input ofoperational amplifier 326 and has its gate coupled to a control signalX!. The relative timing of the control signals X, Y, Y! and S is shownat the right side of FIG. 10. The difference in diode voltage before andafter the timing sequence is amplified by the circuit gain and appearsat the output of the operational amplifier 326, corresponding to theabsolute temperature.

Persons of ordinary skill in the art will appreciate that the actualcurrent source and sink levels, supply voltage values circuit gains canbe changed without changing the nature of the circuit operation. Inaddition, such skilled persons will realize that, while a single-endedcircuit is shown in FIG. 10, a differential circuit could be used tomeasure the voltage across the diode.

Referring now to FIG. 11, the operation of gate driver circuit 234 ofFIG. 7 is explained in more detail. External power MOSFET 340 has itssource coupled to supply potential 342. Its gate is coupled to I/O pad232 and its drain is coupled to I/O pad 212 or 192 (see FIG. 7). Ifsupply potential 342 is positive, power MOSFET 340 will be a p-channeldevice and if supply potential 342 is negative, power MOSFET 340 will bean n-channel device. Resistor 236 or 238 (again see FIG. 7) may bedisposed in the SOC device and is used to assure that the power MOSFET340 will be turned off unless a gate drive signal is supplied at I/O pad232.

Operational amplifier 344 drives the gate of p-channel MOS gate-drivetransistor 346. The drain of p-channel MOS gate-drive transistor 346 iscoupled to I/O pad 232. The source of p-channel MOS transistorgate-drive 346 is coupled to a positive supply potential throughp-channel MOS enable transistor 348. The non-inverting input ofoperational amplifier 344 is coupled to the drain of power MOSFET 340via I/O pad 192 (or 212) through resistor 350. The inverting input ofoperational amplifier 348 is coupled to capacitor 352 driven byconstant-current source 354.

Similarly, operational amplifier 356 drives the gate of n-channel MOSgate-drive transistor 358. The drain of n-channel MOS gate-drivetransistor 358 is coupled to I/O pad 232. The source of n-channel MOStransistor gate-drive 358 is coupled to a negative supply potentialthrough n-channel MOS enable transistor 360. The inverting input ofoperational amplifier 356 is coupled to the drain of power MOSFET 340via I/O pad 192 (or 212) through resistor 340. The non-inverting inputof operational amplifier 356 is coupled to capacitor 362 driven byconstant-current source 364. The non-inverting input of operationalamplifier 344 and the inverting input of operational amplifier 356 arecoupled to ground through resistor 366.

In the example shown in FIG. 11 where an n-channel MOS power transistor340 is to be driven, p-channel enable transistor 348 is turned on. Toturn on n-channel MOS power transistor 340, current source 354 is turnedon and charges capacitor 352 at a linear rate. The voltage on capacitor352 is amplified with a negative gain, producing a decreasing rampvoltage at the output of operational amplifier 348. This causes adecreasing ramp voltage at the drain of p-channel gate drive transistor346 to turn on p-channel MOS power transistor 340. The final gatevoltage on the MOS power transistor 340 is established by the IR dropacross the gate-to-source resistor 236 or 238 and is determined by thecurrent through the p-channel enable transistor 348. If it is desired toturn on a p-channel MOS power transistor, n-channel enable transistor360 is turned on, current source 364 is turned on and charges capacitor362 at a linear rate. The voltage on capacitor 362 is amplified with apositive gain, producing an increasing ramp voltage at the output ofoperational amplifier 356. This causes an increasing ramp voltage at thedrain of n-channel gate drive transistor 358 to turn on the p-channelMOS power transistor. The feedback provided to the operationalamplifiers 344 and 356 through resistor 350 assures controlled ramprates on the load.

Referring now to FIG. 12, illustrative embodiments of internal interfacecircuits 130 (FIG. 5) that are particularly useful for the SOC of thepresent invention are shown. Persons of ordinary skill in the art willobserve that the circuits shown in FIG. 12 are illustrative only and notlimiting. Such skilled persons will appreciate that other interfacecircuits may be used.

Internal interface circuit 130 (FIG. 5) may include a plurality of“tiles”, each having a plurality of different types of interfacecircuits. For the purposes of this disclosure, a “tile” is a layoutsubunit where the inputs and outputs are placed in the same physicallocations to allow for modular chip design. More than one of each typeof circuit may be included in each tile, the exact number of each beinga matter of design choice.

For example, a pair of buffers 370 and 372 may be provided. Buffers 370and 372 are shown in FIG. 12 having their inputs coupled together andhaving their outputs independently connectable. Buffers 370 and 372 actas input buffers for the FPGA core.

Internal interface circuit 130 may also include inverting buffer 374disposed between an input node 376 and an output node 378. A firstprogrammable element 380 is coupled between the input of buffer 374 andthe output node 378. A second programmable element 382 is coupledbetween the output of buffer 374 and the output node 378. To bypassbuffer 374, programmable element 380 is programmed and programmableelement 382 is left unprogrammed, connecting input node 376 directly tooutput node 378. To place the buffer 374 in the circuit, programmableelement 382 is programmed and programmable element 380 is leftunprogrammed, coupling input node 376 to output node 378 through buffer374. Buffer 374 acts as an output buffer for the FPGA core.

In addition, a pair of programmable elements 384 and 386 may beconnected in series between a logic-high voltage potential and alogic-low voltage potential. The common connection between theseprogrammable elements is used as an output node 388 to drive, forexample, the gate of transistor 348 or 360 in FIG. 11, or at least oneof the control lines of multiplexers 186 196 216 of FIG. 7.

According to an illustrative embodiment of the invention, power for theanalog portion of the ADC 136 may be 3.3V. The analog I/O circuits mayalso employ a +/−3.3V supply. These supply voltages may be generated onchip from the 1.5V V_(CC) power supply using charge pump circuits in amanner known in the art. Alternatively, 3.3 volts may be supplied to theSOC and 1.5 volts may be generated on chip by regulating down from the3.3 volts.

A high-precision voltage is needed as a reference voltage input to theADC 136 or may be generated within the ADC 136. This voltage may bescaled from an on chip Bandgap voltage source using known techniques.Such a bandgap reference is shown in FIG. 13. A first grounded-base PNPtransistor 390 has a resistor 392 coupled between its emitter and theoutput of operational amplifier 394. A second grounded base pnptransistor 396 has a pair of resistors 398 and 400 coupled between itsemitter and the output of operational amplifier 394. The emitter oftransistor 390 is coupled to the non-inverting input of operationalamplifier 394 and the common connection of resistors 398 and 400 iscoupled to the inverting input of operational amplifier 394. The outputvoltage V_(ref) of the operational amplifier 394 is given by theexpression shown in FIG. 13.

A separate power source for the bandgap reference is useful for reducingthe risk of coupling noise from FPGA sources. The output of the bandgapreference may also be used for controlling the level of on-chipgenerated analog supplies. The output of the bandgap reference may besupplied to the non-volatile memory (NVM) blocks if the particular NVMbeing used requires a stable reference voltage (e.g., for the senseamplifiers). The bandgap reference circuit is used to generate areference voltage that will be used by other analog blocks as well asthe ADC 136 of FIG. 5. The operational amplifier 394 is not necessarilybut advantageously powered by a 3.3V charge pump. Although the V_(ref)output of the circuit is voltage-, process-, andtemperature-independent, the minimum voltage supply required by theoperational amplifier is about 1.35V. Hence it is preferably supplied bya 3.3V charge pump and not by 1.5V V_(CC).

Referring now to FIG. 14, ADC 136 of FIG. 5 is shown in more detail. ADC136 may be a capacitor-based successive approximation (SAR) ADC as isknown in the art. The ADC 136 is divided into two portions, an analogportion 410 and a digital portion 412. The analog portion 410 containsan analog multiplexer 414, capacitor array 416 and a comparator 418. Thedigital part contains successive approximation register 420, clockdivider 422, and conversion control logic 424. Also, as is known in theart, calibration logic 426 is coupled to a calibration capacitor array428.

In the illustrative example shown in FIG. 14, the analog multiplexer 414chooses one out of 32 input channels. Once a channel is selected usingthe multiplexer select lines, it charges the main capacitor array 416during the sample phase. After that the sampled input that charged thecapacitor array is compared to a known voltage and based on the compareresult the capacitors are switched according to the successiveapproximation algorithm. When the two inputs of comparator 418 areequal, the data in the successive approximation register 420 is thedigital equivalent of the analog input. Clock divider and sample time(which are programmable) determine the speed of this conversion.

Referring again to FIG. 5, system supervisor master 140 is intended toprovide all chip-level and system level power-on/initialization/resetfunctions. The power-up control circuit includes circuitry for managingthe SOC device during power-up, as will be described in more detailbelow.

The analog power supply circuitry may include known power supply andmanagement circuits, for supplying the required voltages for operationof the various circuit blocks of the SOC device, as well as differentvoltages for programming the programmable elements of the SOC device. Inthe embodiment shown in FIG. 5, the programmable logic block and digitalhardwired blocks have their own power supply circuits separate from thesystem controller circuit block. In this embodiment, the systemcontroller circuit does include an analog power supply circuit block144. The analog power supply circuit block 144 supplies power to theanalog blocks as well as performing power monitoring functions formonitoring the power input to all blocks on the SOC device. The analogpower supply circuitry includes voltage monitoring circuits, chargepumps, and voltage supply circuitry. These types of circuits are allknown in the art and are used on other types of semiconductor devices,such as ASICs.

The analog power supply circuitry 144 includes a voltage conversion andsupply circuit block that may include, for example, voltage referencecircuits, charge pumps, switching supplies, switch regulators,buck/boost regulators, and voltage regulators. Use of such circuits isknown by those skilled in the art. Different circuit blocks in the SOCdevice may require different voltages, and these voltages may bedifferent from the voltage supplied by the system of which the SOCdevice is a part. The voltage conversion and supply circuitry may beimplemented, therefore, to provide the required power to the variouscomponents, as is known in the art. Once the voltage input to the devicehas been stepped up or stepped down, if required, via the circuitsdiscussed above, the required voltages are provided to the variouscomponents of the SOC device via hardwired power lines.

In the illustrative example of this disclosure, the voltage input to thedevice may be 3.3V, but the hardwired analog circuit blocks may require1.5V so the voltage conversion and supply circuitry steps the deviceinput voltage (V_(CC)) down to 1.5V in order to supply the digitalcircuits with the proper voltage. In the alternative 1.5 volts could besupplied to the SOC and pumped up to 3.3 volts. In the embodiment shownin the figure, other elements of the SOC, such as the programmable logicblock and the non-volatile memory block have separate voltage conversionand supply circuitry that is not included in the system controllercircuit block.

The analog power supply circuitry 144 also includes a voltage monitoringcircuit for comparing an input voltage to a reference voltage, as isknown in the art. The voltage monitoring circuit receives a voltagereference signal (e.g., a bandgap reference signal from a voltagereference circuit, described below) as an input and uses it to compareother voltage supplies (e.g., the programmable logic block voltagesupply, the non-volatile memory voltage supply, and the analog voltagesupply) on the SOC device to the bandgap reference. If the voltages ofthe monitored supplies do not compare favorably with the referencevoltage (i.e., are outside a predetermined error range), the voltagemonitoring circuit may output a signal indicating the problem. Theoutput error signal could be used to delay start-up, trigger power down,generate one or more resets, assert an interrupt, or shut down operationof the SOC device.

A voltage reference circuit 146 included in the system controllercircuit may be, for example, a bandgap reference circuit like the onedescribed previously with reference to FIG. 13, or other type of circuitknown in the art for supplying an accurate reference voltage. A bandgapreference circuit provides an absolute voltage output for reference byother circuits on the SOC device. Other power supplies can be comparedto the reference voltage, as described above. The voltage referencecircuit 146 may include other circuitry, for example, operationalamplifiers and buffers to change the level of the voltage. Bandgapvoltage reference circuits other than the one illustrated in FIG. 13 maybe used in other embodiments of the invention, such as, for example abandgap voltage reference circuit available from QualCore Logic, Inc, ofSunnyvale, Calif. that may be adapted for use in the particular SOCdevice. This bandgap voltage reference circuit may be separate from thegeneral bandgap voltage source used for other circuit blocks on the SOCdevice, such as the programmable logic block, in order to provide ahigh-precision voltage input for components such as the ADC circuit, andto reduce the risk of coupling noise from other circuits.

The power-up control circuit 142 controls the internal power-up sequenceof the SOC device. The power-up sequence is used to insure that circuitsreceive the proper initialization, in the proper order, as power issupplied to the device. A typical power-up sequence is shown in thestate-machine diagram of FIG. 15A. Use of such a sequence reduces thechance for errors or damage to the SOC device resulting from circuitsoperating at an improper voltage (e.g., insufficient voltage orexcessive voltage due to a spike) or to an improper sequence (e.g., anactive circuit trying to communicate with a circuit that is not yetinitialized. The power-up control circuit 142 includes circuits thatdetermine whether sufficient voltage is present to activate a circuitduring power-up. These circuits can also be used to monitor the samevoltages during operation of the SOC device, in addition to monitoringvoltages during power-up. A timing diagram showing a typical startupsequence is shown in FIG. 15B.

A power-up control circuit 142 implementing a power-up sequence such asthe example described herein may be implemented in hardwired circuitry,or a combination of hardwired circuitry and programmable logic. As isknown in the art, regulator circuits, charge pumps, voltage referencegenerators, etc. must be implemented in hardwired circuits, whilesequence and control circuits may be implemented in hardwired circuitsor programmed in programmable logic, as long as they are not required tobe used before the programmable logic block is active.

As shown in FIG. 16, a more detailed block diagram of system supervisormaster block 140 from FIG. 5, the power-up control circuit 142 is shownto be comprised of circuits employing standard circuit elements toprovide signals to activate various elements of the SOC device when theproper conditions are met (e.g., timing, sufficient voltage, etc.). Inthe embodiment shown in FIG. 16, the power-up control circuit includes avoltage-reference-good circuit 440 for indicating that the circuitsupplying the reference voltage is active and functioning withinpredetermined parameters. The power-up control circuit also includescircuits 442 and 444 for indicating that each voltage supply (3.3V and1.5V, in the example shown) is good (meaning active and functioningwithin predetermined parameters). The power-up control circuit may alsoinclude voltage filter circuits for filtering voltages supplied tovarious components of the SOC device, such as, for example, the Vddfilter circuit 446 shown in FIG. 16.

In addition to verifying and managing the power supplies, the power-upcontrol circuit includes circuitry for activating various components ofthe SOC device such as the programmable logic block (circuit 448) andthe non-volatile memory block (circuit 410), determining whether thecomponent has become active, and outputting a signal to indicate thatthe circuit has become active. The signal indicating that a component isactive may be used to activate the next step in the power-up sequence.Also shown in FIG. 16 are circuits for managing the power-up functionsof the ADC. Specifically, the ADC-reference-good circuit 412 indicatesthat the reference voltage input to the ADC is accurate, andADC-calibrate circuit 414 to indicates that the ADC is calibrated.

The particular circuits used in actual embodiments of the presentinvention embodiments will depend on the particulars of the programmablelogic, memory, analog, and digital hardwired blocks employed in theparticular device. Examples of standard circuits that may be adapted toperform the power-up control functions are multiplexers, controlcircuits, power monitor circuits, crystal oscillators, bandgap referencecircuits, operational amplifiers, instrument amplifiers, charge pumps,filters, power supply regulators, known in the art and available fromcircuit design and IP licensing companies such as QualCore Logic, Inc.,Sunnyvale, Calif.; TriCN, Inc., San Francisco, Calif.; or SliceX, Inc.,Salt Lake City, Utah.

FIG. 17 shows a portion of the power-up control circuit 460 forperforming functions early in the power-up sequence. Also shown in FIG.17 is the voltage reference (bandgap) circuit of FIG. 13 incommunication with the power-up circuits. For illustration purposes, thepower-up circuits shown in FIG. 17 are a 1.5 volt regulator circuit 462for supplying 1.5 volts to the digital circuitry of the SOC device, a−Ve charge pump circuit 464 for supplying a negative voltage for thehardwired analog circuits of the SOC device, and a Vdd filter circuit466 for providing a filtered 3.3 volt source to circuits requiring afiltered voltage (e.g., the bandgap voltage regulator circuit).

More particularly, 3.3V is supplied to the SOC through I/O pad 468 andis supplied to 1.5 volt regulator circuit 462 as shown. As can be seenfrom FIG. 17, I/O pad 468 is also coupled to −Ve charge pump circuit 464and to Vdd filter circuit 466. The 1.5V output of 1.5 volt regulatorcircuit 462 drives the base of external emitter-follower NPN transistor470 through I/O pad 472. The output of the external transistor 470 isfed back to 1.5 volt regulator circuit 462 via I/O pad 474. Comparator476 produces the 3.3V supply good signal when the voltage on I/O pad 474is above the value set by the voltage from the 1.5 volt regulator 462.Comparator 478 produces the 1.5V supply good signal when the voltage onI/O pad 474 is above a preset value derived from the voltage at I/O pad474.

The output of −Ve charge pump circuit 464 is presented at I/O pad 480and the output of Vdd filter circuit 466 is presented at I/O pad 482.

As shown in the power-up sequence flow chart of FIG. 15A, the firstsignal produced in the power-up sequence is the bandgap-good signal.This signal indicates that the bandgap reference circuit is outputtingthe accurate, regulated voltage for which it is designed. Since thisvoltage is the reference for the other circuits on the device, it is thefirst required to be operational during power-up. As power input to thebandgap circuit increases during power-up, the voltage output by thebandgap circuit almost exactly matches the input voltage until the inputvoltage rises above the voltage the bandgap circuit is designed tooutput (“reference voltage”). The reference voltage for the device isgenerally below the input voltage (Vcc) of the SOC device. For example,the reference voltage for the SOC device may be 1.2V where Vcc for theSOC device is 3.3 volts.

The portion of the power-up control circuit shown in FIG. 17 alsoincludes a threshold p-channel MOS transistor 484 and a small currentsource 486 for indicating when the bandgap reference circuit 488 isoutputting the correct bandgap output voltage. In the example shown inFIG. 17, the bandgap circuit 488 receives a voltage input from the Vddfilter circuit 466 and outputs a controlled voltage via an output 490.The source of threshold transistor 484 is coupled to the Vdd filtercircuit output, and a buffer 500 and the current source 486 areconnected to the drain of threshold transistor 484. The gate of thethreshold transistor 484 is connected to the bandgap output 490. In thisconfiguration, the threshold transistor 484 will turn on when thevoltage input to the bandgap circuit 488 exceeds the bandgap circuitoutput by the threshold of the p-channel threshold transistor 484. Oncethe threshold transistor 484 turns on, current flows through thethreshold transistor 484 and the bandgap-good signal is activated, viathe buffer 500. This insures that the bandgap circuit 488 will not beindicated as active until it is outputting the proper reference voltage.

The threshold of the threshold transistor 484 may be designed to apredetermined value by varying the geometry and materials of thetransistor, as is known in the art. Although the exact threshold mayvary with temperature, the transistor can be designed so any variancewill not interfere with the basic functionality of the circuit. Thisfunctionality can be maintained as long as the general input voltage forthe device sufficiently exceeds the reference voltage. A small currentsource 486, on the order of 1 μA, connected between the buffer 500 andground insures that the current through the threshold transistor 484 issufficient before the bandgap good signal is activated at the output ofbuffer 500. Once the bandgap good signal is activated, indicating thatthere is an accurate reference voltage available on the device, theother circuits in the power-up control circuit can begin theiroperations, for example, by comparing their input voltages to the knowngood reference voltage.

The system controller circuit block 140 also includes a systemsupervisor circuit. The system supervisor circuit may be implemented inhardwired circuits, programmed into programmable logic, or a combinationof both. The system supervisor circuit block 148 manages on-chip andoff-chip signals following the power-up of the SOC device. Once the SOCdevice is powered up and active, the system supervisor circuit block mayperform power-up management of the system of which the SOC device of thepresent invention is a part, and provide other system managementfunctions such as managing voltage monitoring circuits to monitor systemvoltages during operation. The system supervisor block may communicatewith off-chip devices via, for example, a hardwired JTAG interfacecircuit block 124 included in the system controller circuit block 140, ahardwired interface designed in accordance with another interfacestandard, or via the general purpose I/Os of the SOC device.

The system supervisor 148 may use, for example, known circuits such as amicroprocessor, a microcontroller, or a system control state machinethat are either hardwired or programmed into the programmable logicportion of the SOC device using circuit design and programmingtechniques known to those skilled in the art. These known circuitsperform system management functions such as power-up sequencing ofoff-chip devices, system clock enabling, and system reset, as is knownto those skilled in the art. In addition, known level compare circuits,filter circuits, and external device control circuits may be implementedin either programmable logic, or hardwired into the SOC device to addfunctionality to the system controller. The particular embodiments ofthe system supervisor circuit will be highly dependent on the usersystem, and therefore it is desirable to implement much of the circuitin programmable logic. For example, different user systems may havedifferent numbers of power supplies, operating at various voltages, tobe monitored. The user can configure the system supervisor circuit toaccommodate the parameters of the user's particular system.

For example, the system supervisor circuit 148 may be configured toinclude a specialized microcontroller-type circuit for power-up andpower monitoring called an ADC sequencer circuit. System voltages, aswell as the reference voltage, may be input to the ADC, which convertsthe voltages to digital values that are input to the programmable logicblock. An ADC sequencer circuit programmed into the programmable logicblock may compare the digital values and use the results to controlsystem elements via signals output from the SOC device (e.g., power-upenable signals, etc.).

While embodiments and applications of this invention have been shown anddescribed, it would be apparent to those skilled in the art that manymore modifications than mentioned above are possible without departingfrom the inventive concepts herein. The invention, therefore, is not tobe restricted except in the spirit of the appended claims.

1. A system controller circuit for a programmable system-on-a-chipcomprising: a power-up control circuit; a voltage reference circuit; ananalog power supply circuit; a system supervisor circuit; wherein: thepower-up control circuit and analog power supply circuit each receive avoltage reference signal from the voltage reference circuit; and thesystem supervisor circuit sends signals to the power-up control circuitand the analog power supply circuit to control at least one of power-upsequencing of off-chip devices, power-up sequencing of on-chip devices,system clock enabling, and system reset.